Golf is a game in which a player, using many types of clubs, hits a ball into each hole on a golf course in the lowest possible number of strokes. Golf club head manufacturers and designers seek to improve certain performance characteristics such as forgiveness, playability, feel, and sound. In addition, the durability of the golf club head must be maintained while the performance characteristics are enhanced. In general, “forgiveness” is defined as the ability of a golf club head to compensate for mis-hits where the golf club head strikes a golf ball outside of the ideal contact location. Furthermore, “playability” can be defined as the ease in which a golfer can use the golf club head for producing accurate golf shots. Moreover, “feel” is generally defined as the sensation a golfer feels through the golf club upon impact, such as a vibration transferring from the golf club to the golfer's hands. The “sound” of the golf club is also important to monitor because certain impact sound frequencies are undesirable to the golfer.
Golf head forgiveness can be directly measured by the moments of inertia of the golf club head. A moment of inertia is the measure of a golf head's resistance to twisting upon impact with a golf ball. Generally, a high moment of inertia value for a golf club head will translate to a lower amount of twisting in the golf club head during “off-center” hits. Because the amount of twisting in the golf club head is reduced, the likelihood of producing a straight golf shot has increased thereby increasing forgiveness. In addition, a higher moment of inertia can increase the ball speed upon impact thereby producing a longer golf shot.
The United States Golf Association (USGA) regulations constrain golf club head shapes, sizes, and moments of inertia. Due to theses constraints, golf club manufacturers and designers struggle to produce a club having maximum size and moment of inertia characteristics while maintaining all other golf club head characteristics, such as weight and sufficient durability.